Frederic Manby

Place: a motorway. Time: one of those occasions when you see stranger cars. Like: a colourful cavalcade of Vauxhalls from the Vectra Enthusiasts Club. A Saab convertible with the roof down. A Subaru Tribeca. An old XJ6 in police livery. An Audi obeying the speed limit. I was in it. The car you see here. The latest 5 Cabriolet, a four-seater delight, even in bridal white.

Actually, more cars are obeying speed limits. Even Audi drivers. The message has struck: “smart” motorways use technology to keep us moving smoothly and rat on us if we are having too much speed.

What margin are we allowed? Ten per cent? I don’t think so. A sage in the Camshaft Arms reported getting a summons for 42mph in a 40mph zone in the wee small hours on a straight stretch of rural road. He took the droll insult with grim humour and attended a speed awareness course.

The A5 had devices to restrain me. There was cruise control and a speed limiter and adaptable distancing to the car in front. Cruise control can be a mixed blessing, best kept for light traffic where you don’t need to interact with faster/slower vehicles.

Anyway, the sun was out and at 70mph the open A5 was very pleasant. It has a tonneau which you can fasten over the empty seats to improve air flow. I didn’t bother and the cabin remained reasonably unruffled. It’s a beautiful car, the acme of the current state of quality convertibles. If there was body shudder I didn’t notice but it’s a safe bet that the A5 coupe is stiffer.

You can buy the cabrio with a 349bhp 3-litre petrol V6, capable of 0-60 inside five seconds and soothe your green credo with laboratory economy of 36mpg and 177g of CO2. It costs £51,835 and will be far thirstier.

The weakest petrol engine is a 2-litre giving 187bhp and 0-62 in 7.9 seconds, 48mpg and 136g with manual gears, from £35,235. With the 2-litre diesel you get 187bhp but much more torque, automatic S tronic gears and the dreamy prospect of nearly 63mpg and just 118g of nasty carbon. Price: from £39,075. There’s also a 3-litre V6 diesel automatic with 215bhp, quattro 4x4 drive, masses of torque and quoted at 6.8 seconds for the sprint, 57.6mpg and 128g, from £44,240.

The familiar comparison between speed limits and excessive performance apply. Even the entry model is fast enough and this engine is offered with all trim levels – SE, Sport (£37,175) and the popular S-line (£38,785). You can also have it with the double clutch S tronic seven-speed gearbox with front or all wheel drive.

Audi sent me the other four cylinder petrol model, the 248.5bhp quattro S tronic S line at £45,630 – also offered in Sport trim at £43,980. The figures for this are 0-62mph in 6.3 seconds, 144g and 44.8mpg on 17-inch wheels. Doesn’t that sound good? The demo car was on no-cost 19s with Hankook tyres which add 5g to the CO2 rating. Other extras included a rear-view camera (£450) and the virtual cockpit which allows you to switch displays and incorporate a full width navigation view in the main instrument area – shrinking the size of the rpm and mph dials. You can drive without it, but at £1,150 you’ll be tempted.

The cabrio-exclusive, tofana white paint added £645. It shares its name with peaks in the Dolomites. However, in 17th century Italy there was a notorious poisoner named Giulia Tofana who sold her potions to women wishing to be free of their husbands. When she got the chop they had done for several hundred men. Let’s go with the snowy peaks. No-cost paints on this car are just ibis white or black.

The new cabrio is a cracking car. It retains a multi-layer insulated folding fabric roof, offered in red, black, graphite and brown. A one-touch button now takes care of folding in 15 seconds or erecting in 18 seconds. You can do this while moving at urban speeds. It goes into a compartment in the boot, which retracts to maximise luggage space when the roof is up. Even with it down I carried a bicycle under the compartment, after folding forward the rear seats by triggering them from the boot.

Heated front seats are supplied, as are extension speakers in the seat belts to counteract wind roar. SE kit also includes part leather, part fake known as twin leather. Sport grade adds navigation, powered sport seats and LED interior lighting. S line brings 18 inch wheels, LED headlights, various detail conceits, lower and stiffer suspension with the option of ordering it with comfort suspension or with selectable settings. You can specify an auxiliary hot air duct for topless driving when you need more cabin heat. Other options include semi-autonomous driving with which, under safety parameters, the car will accelerate, brake, steer and advise on obstacle avoidance.